The present disclosure relates to an information processing apparatus, an information storage apparatus, an information processing system, an information processing method, and a program. More particularly, the present disclosure relates to an information processing apparatus, an information storage apparatus, an information processing system, an information processing method, and a program for preventing fraudulent usage of contents.
Contents such as a movie and a music piece are provided to users via various media such as a DVD (Digital Versatile Disc), a Blu-ray Disc (trademark), and a flash memory, networks such as the Internet, or a broadcast wave. The users can reproduce such contents by using a recording/reproducing apparatus such as a PC, a mobile terminal, a BD player, or various information processing apparatuses such as a television.
However, copyrights, distribution rights, and the like of many of the contents to be provided to users, such as music data items and image data items are held by creators or sellers. Thus, in many cases, providers of such contents set predetermined usage restriction on the contents when providing the contents to the users.
By using digital recording apparatuses and digital recording media, for example, images and sound can be repeatedly recorded and reproduced without being deteriorated. Thus, there has been a problem of spread of usage of illegally copied contents, specifically, distribution of illegally copied contents via the Internet and distribution of what is called pirated discs.
In order to prevent such illegal data copying, various technologies for preventing illegal copying to digital recording apparatuses and digital recording media have been put to practical use.
As an example of such technologies, there is a content encryption process of giving a key to decryption of an encrypted data item only to a reproducing apparatus having a license which is a content usage right. The license is given to a reproducing apparatus designed to follow predetermined operating regulations such as a regulation prohibiting illegal copying. Thus, other reproducing apparatuses to which the license has not been given do not have the key to decryption of an encrypted data item, and hence cannot decrypt the encrypted data item.
However, even when such content encryption is executed, contents have still been fraudulently used.
Here, an example of fraudulent usage of contents is described.
In this example, a configuration is assumed in which a content server distributes encrypted contents to user apparatuses such as a recording/reproducing apparatus, a PC, and a mobile terminal.
When distributing encrypted contents to the user apparatuses, the content server distributes the following data items to the user apparatuses, for example, via a network.
(a) Encrypted contents
(b) Encryption keys to encryption and decryption of the encrypted contents.
When distributing the same content such as the same movie to a large number of user apparatuses, the content server executes, for example, in either one of the following two processes.
(A) Creating different encrypted contents through application of individual different encryption keys, and providing the different encrypted contents respectively to the user apparatuses.
(B) Creating the same encrypted content encrypted with the same encryption key, and providing the same encrypted content to each of the plurality of user apparatuses.
In consideration of security for preventing fraudulent usage of contents, the above-mentioned process (A) is advantageous.
However, in order to execute the above-mentioned process (A), it is necessary to execute a process of setting individual encryption keys respectively to a large number of users and creating individual encrypted contents. As a result, there arises a problem that, in proportion to the number of users to receive contents, processing load to the server becomes higher owing, for example, to creation and management of the encryption keys, and the process of creating the encrypted contents.
Thus, in many cases, the above-mentioned process (B), in other words, a process of creating the same encrypted content of the same content by encryption with the same encryption key and providing the same encrypted content to each of the plurality of users is performed.
For example, one encryption key (in other words, title key) is set with respect to a content having a certain title, and the same encrypted content is created through application of the one encryption key. Then, the following data set is distributed to each of the large number of users.
(a) Encrypted content
(b) Title key
Such a process reduces the processing load to a content server.
Note that, in the following description, encryption keys set in units of titles of contents are defined as “title keys.”
Note that, the title keys are applied to processes of encrypting and decrypting encrypted contents corresponding to the titles.
However, when the same data sets, in other words, the same combinations of the following data items:
(a) Encrypted content, and
(b) Title key,
are distributed to the large number of users in this way, some “unauthorized users” may execute the following processes.
Specifically, fraudulence as follows may be performed.
(1) An “unauthorized user” reads a title key received from a server, and exposes the read title key to an unspecified number of users.
Alternatively, (2) an “unauthorized user” uses a title key A corresponding to a certain encrypted content A so as to encrypt a whole different content B, and distributes the following data combinations to an unspecified number of users.
(X) Title key A
(Y) Encrypted content B encrypted with the title key A.
For example, in a case where the above-mentioned process (1) is executed, a large number of users who have acquired the illegally exposed title key fraudulently use the content encrypted with the same title key as the illegally exposed title key.
Further, in a case where the above-mentioned process (2) is executed, when the large number of users acquire, from the above-mentioned “unauthorized user,” the illegal data set, in other words,
(X) Title key A, and
(Y) Encrypted content B encrypted with the title key A, which are created by the “unauthorized user,” the encrypted content B is illegally used.
As a result, fewer users legally purchase an original legal data set, in other words,
the encrypted content B, and
a title key B corresponding to the encrypted content B, and profit to copyright holders and distribution right holders are markedly lost.
Further, a specific example of the fraudulent process is described.
In this specific example, it is assumed that the content server holds the following data sets of encrypted contents (C) of items (1) to (3) and title keys (Kt).
(1) (Kt11, C11)
(2) (Kt12, C12)
(3) (Kt13, C13)
Note that, Cnn represents a content file, and
Ktnn represents a title key used for encryption of the content.
(Kt11, C11) represents a data set of a title key (Kt11) and a content (C11) encrypted with the title key (Kt11).
For example, it is assumed that a certain “unauthorized user Ux” has purchased all the above-mentioned three data sets:
(1) (Kt11, C11),
(2) (Kt12, C12), and
(3) (Kt13, C13), and
that this purchasing process itself has been executed based on a predetermined legal purchasing procedure between a user apparatus such as a PC of the “unauthorized user Ux” and a content server.
The “unauthorized user Ux” records the above-mentioned data sets (1) to (3) to a medium such as a hard disc of the PC as a user apparatus.
The “unauthorized user Ux” reads the above-mentioned data sets (1) to (3) from the medium such as a hard disc of the PC as a user apparatus, and decrypts all the encrypted contents with respective title keys. In this way, the following data items are acquired.
Title keys: Kt11, Kt12, and Kt13
Decrypted contents: C11, C12, and C13
Note that, when a regular content reproduction program is used in an authorized reproducing apparatus, title keys cannot be read to the outside. However, the title keys may be read, for example, by installing a malicious program to the apparatus itself such as the PC. Thus, it has still been difficult to perfectly prevent the title keys from being read.
Further, the “unauthorized user Ux” creates a data item
C11∥C12∥C13
acquired through concatenation of the decrypted contents: C11 to C13, and encrypts this concatenated data item with the title key: Kt11.
In other words, the “unauthorized user Ux” creates the following data set
(Kt11, C11∥C12∥C13),
and illegally distributes this data set via a network. Specifically, this data set is sold at low price, or provided for free to a large number of users.
Such a process allows the large number of general users to acquire, from the above-mentioned “unauthorized user Ux,” the above-mentioned illegally created data set, in other words,
(Kt11, C11∥C12∥C13).
This data set contains the following data items:
(a) Encrypted contents encrypted with the title key Kt11, and
(b) Title key Kt11,
and has the same data structure as that of a data set content provided from an authorized content provider to a user.
Thus, as long as having a licensed regular content reproduction program, any authorized reproducing apparatus can decrypt and reproduce the encrypted content [C11∥C12∥C13] without any problem by using the title key Kt11.
As a result, contents are fraudulently used more and more without being legally purchased. In this example, fewer users legally purchase the contents such as C11 to C13. Ultimately, profit to legal right holders is lost.
Here, this fraudulent process is more specifically described. For example, it is assumed that, with regard to series contents such as a drama of twelve titles of Episode 1 to Episode 12, purchase units of the contents are set in units of the episodes as follows.
Episode 1=(Kt01, C01)
Episode 2=(Kt02, C02)
Episode 3=(Kt03, C03)
. . .
Episode 12=(Kt12, C12)
In such a case, a certain “unauthorized user” may execute the following process: purchasing the entire series, in other words, all the twelve titles of Episode 1 to Episode 12; concatenating the contents corresponding to Episode 1 to Episode 12: C01 to C12; and creating a data set by re-encryption with the title key corresponding to Episode 1, in other words,
(Kt01, C01μC02∥C03 . . . ∥C12)
so as to expose this data set on the network or illegally sell the same.
In such a case, a large number of user apparatuses are allowed to reproduce and use the contents by acquiring the fraudulent data set
(Kt01, C01∥C02∥C03 . . . ∥C12)
created by the “unauthorized user.”
For example, on the assumption that a full price in episode units of each of the above-mentioned twelve episodes is ¥2,000, purchase of all the twelve episodes costs as follows.12×¥2,000=¥24,000
When the “unauthorized user” sells, for example, at ¥6,000, the fraudulent data set
(Kt01, C01∥C02∥C03 . . . ∥C12),
a large number of users are allowed to purchase this lower-price content. As a result, legal sale of contents is hindered, which leads to profit loss and infringement of rights of original copyright holders and distributorship holders.
Other than the above-mentioned example, the title key Kt11 that has been set correspondingly to a certain content C11 may be used for encryption of various other irrespective contents Cxx as the following data set.
(Kt11, Cxx)
The contents Cxx may include various contents, and hence there arises a problem that all the contents can be limitlessly decrypted and reproduced with a single title key.
In other words, even when a reproducing apparatus prohibited from reproducing plaintext contents is used, by using the above-mentioned fraudulent data set, decryption and reproduction can be executed just as legally purchased contents are decrypted and reproduced.
Further, the “unauthorized user” is allowed also to offer replacement and re-encryption of title keys as services, and hence is allowed to behave just as an authorized server.
As described above, it has been difficult to prevent fraudulent usage only with such a content encryption process as a countermeasure.
As a method of eliminating fraudulent usage of contents other than the encryption process, there is a method of causing a reproducing apparatus to verify whether or not contents have been tampered. By employing this method, in a case where some alteration (tampering) has been confirmed in a content, for example, during a process of distributing the content, usage of the tampered content can be canceled.
Specifically, the following control system may be employed: permitting reproduction of contents only in a case where a user apparatus to execute reproduction of contents is caused to execute a process of verifying whether or not a content has been tampered and no tampering has been confirmed in the content; and cancelling reproduction of contents in a case where some tampering has been confirmed in the content.
For example, Patent Document 1 (Japanese Patent Application Laid-open No. 2002-358011) discloses a control system: calculating a hash value from a file of a content to be reproduced; executing comparison of this hash value with a prepared verification hash value, in other words, a verification hash value calculated in advance based on a regular content data item; and shifting to a process of reproducing the content in a case where the newly calculated hash value has matched the verification hash value and it has been judged that no tampering has been confirmed in the content.
However, in the case of executing such a process of calculating a hash value based on a content, when a volume of a content data item as a source data item of a calculation of the hash value is large, excessively high processing load and an excessively long processing time period are required for the calculation. In recent years, qualities of moving images have become higher, and hence, in many cases, one content has a data volume of from few gigabytes to few tens of gigabytes. When the user apparatus to execute reproduction of contents is caused to execute the process of calculating a hash value of a content based on such a large volume data, there arises problems that an excessively high data processing capability is required of the user apparatus and that a content reproducing process is not efficiently executed owing to a longer time period required for verification of contents.
Further, Patent Document 2 (Japanese Patent No. 4576936) discloses a system in which hash values of respective hash units set as segmented data items of contents stored in an information recording medium are recorded to a content hash table, and are stored in the information recording medium together with the contents.
According to the system disclosed in Patent Document 2, an information processing apparatus to execute content reproduction executes a hash value verification process based on at least one of the hash units selected at random. With this system, processes of calculating and verifying the hash values can be executed irrespective of data volumes of contents, specifically, based on a hash unit having a small volume of data. As a result, content verification can be efficiently executed in the user apparatus to execute content reproduction.
However, the system disclosed in Patent Document 2 is designed on the premise of a process on contents stored in an information recording medium. In other words, there is a problem that, although the system disclosed in Patent Document 2 is applicable to a case where not only contents but also hash values are simultaneously recorded, for example, at the time of manufacture of the information recording medium, it is difficult for this system to be applied to contents downloaded, for example, from a server.
Further, Patent Document 1 and Patent Document 2 above each put emphasis on verification of whether or not content have been tampered, and hence have a problem of difficulty in restriction of distribution of illegally copied contents.
As described above, with processes of encrypting contents and verifying whether or not the contents have been tampered in related art, distribution of illegally copied contents or leakage of content encryption keys has not yet been sufficiently prevented.